Like I say, it's what you want out of your engine.
For a 4 banger
lots of HP at High RPM look at a short 4-2-1 header lots of scavaging
Lots 'o torque lower RPM? long individual runners into a single collector.
Exhaust are interesting. Matching them up with intakes and cylinder designs even more....
I got a book about 300 pages just looking at the scientific aspect of designing an exhaust system.
Helps when I cant sleep at night....
Actually Bosch has the best book out there on engine and automobile design.